This invention was developed partitially with support from a Federal Grant. The United States Government might have certain rights to the invention claimed in this Patent.
The present invention relates to the determination of parameters which Identify properties of films, and more particularly to determination of parameters which characterize such as the thickness, color or quality of films deposited onto objects of arbitrary shapes, utilizing spectroscopic ellipsometry as applied to standard shaped objects.
Objects which are to be coated with a material for any purpose, (to effect color and/or to improve its functional surface properties etc.), are often of an arbitrary shape and are constantly translated and/or rotated during the deposition procedure to improve the uniformity of the deposition. Such motion can preclude positioning an ellipsometer system so that a beam of electromagnetic radiation provided thereby can constantly, or even periodically, predictably and reliably be directed into a detector.
With the invention disclosed herein in mind, a Patent Search for relevant art was conducted and provided very little. A Patent to Johnson et al. U.S. Pat. No. 6,278,809 was identified and describes provision of an optical fiber onto which is deposited materials. A combination of monochromatic and Broadband light transmitted through said optical fiber is affected by the deposition in a way which is detectable and determinative of factors such as real time growth rate and film composition, refractive index, thickness, surface roughness etc. U.S. Pat. No. 5,871,805 to Lemelson describes the use of a test blank in a deposition system which is monitored by an ellipsometer to provide information applicable in process control.
A need remains for a method of reliably monitoring and controlling the deposition of materials onto irregular shaped objects.
It is well known to deposit material films onto irregular shaped objects to change their color or surface properties etc., but real time quality control of such depositions remains difficult. Common practice is to simply follow a scheduled routine with little or no real time feedback, which routine typically works. The results of each such batch run are then evaluated after the fact. This can, and does, lead to entire batches of processed objects having to be disposed of, or recycled.
The disclosed invention comprises, in the context of material film deposition onto objects of arbitrary shape, the use of electromagnetic radiation to monitor test objects, which test objects present with other than substantially flat surfaces and typically, symmetry about at least one axis. Presently preferred, but non-limiting test object shapes include cylindrical and spherical. In use a beam of electromagnetism is caused to Interact therewith and enter a detector during a deposition procedure. In use the said test object is placed near to the actual object during a deposition procedure and typically is caused to undergo a similar motion to that of the actual object.
Further, it is specifically noted that one or more such test objects can be affixed to a planetary motion system which periodically positions each of the test objects in the path of the electromagnetic beam such that said electromagnetic beam reflects therefrom and then predictably enters into a detector. It is specifically pointed out that such test objects can be made to spin about an axis of its symmetry to simulate the motion of actual objects under process.
A disclosed method of monitoring the results of material deposition onto objects then comprises the steps of:
a. providing a material deposition system including means for causing a beam of electromagnetic radiation to interact with and reflect from an other than substantially flat surface of an object placed therewithin and enter a detector;
b. placing objects onto which material is to be deposited into said material deposition system, including at least one test object which demonstrates at least one axis of symmetry;
c. optionally causing said at least one test object to rotate about at least one axis of symmetry thereof;
d. causing the material deposition system to deposit material onto the objects and at least one test object; and
e. causing electromagnetic radiation to interact with and reflect from said other than substantially flat surface of said test object, and enter the detector.
Steps d. and e. are beneficially practiced simultaneously.
A variation of the described method provides that more than one test object be placed on a means for sequentially placing them into the path of said beam of electromagnetic radiation, and that said more than one test objects be sequentially entered into the ellipsometric beam.
The at least one test object is preferably of a shape selected from the group consisting of:
cylindrical; and
spherical.
The method of monitoring the results of material deposition onto objects is especially applicable to control of the deposition of material which is appropriate to alter a selection from the group consisting of:
color; and
mechanical properties.
The detector which is positioned to receive the ellipsometric electromagnetic beam outputs information which is used to control the deposition process.
While not limiting, it is noted that the preferred source of electromagnetic radiation which is caused to interact with and reflect from a test object, is an ellipsometer system which is sequentially comprised of, prio to said Test Object a Polarization State Generator comprising:
a polychromatic source of electromagnetic radiation;
a polarizer;
optionally a compensator
and a Polarization State Detector after said test object comprising:
optionally a compensator;
an analyzer; and
a multiple element detector system positioned to
intercept reflected electromagnetic radiation after
said test object.
It is also noted that most ellipsometry is practiced by causing electromagnetic radiation to interact with and reflect from a substrate which has a substantially flat surface. The disclosed invention herein causes electromagnetic radiation to reflect from a test object surface which is other than substantially flat.